Vapor compression heat pumps are in conventional use and are have become commonly used to provide heating and cooling air conditioning in residential service.
While the predominant motive power for such heat pump systems has been electric motor drive means, a combustion engine is an attractive alternative source of motive power for such systems and has seen some use in this setting.
One drawback of vapor compression heat pump systems is that during winter operation the heating capacity decreases as the ambient temperature of the outside air, being used as the source of heat, goes down. At the same time the building heat loss increases and temperature in the internal ambient living space decreases. A common solution to the problem has been the provision of auxiliary electric heaters to meet the requirements of the total heating load during more severe outside temperature and weather conditions.
The main reason for this reduction of heating capability of the heat pump is that the refrigerant compressor cannot pump very much refrigerant vapor at these extreme operating conditions.
When the compressor is driven by a combustion engine the problem is accentuated because whenever the compressor does not draw much power the engine is relatively lightly loaded, compared to total load capacity, and therefore does not produce much unused heat of combustion for translation to space heating.
One of the advantages of a combustion engine heat pump system is the available excess heat of combustion generated in the engine. The heat is useful for wintertime heating augmentation when cold ambient outside air is the heat source. This relieves the requirement for auxiliary heaters.
However when the engine is lightly loaded, the advantages of the combustion engine driven heat pump system are reduced, since the recovery of engine heat useful for heating purposes in the system is limited and there is less heat available at the time when it would be most useful.
It is a common practice in internal combustion engine driven heat pump systems to recover the unused heat from the engine by conveying a working fluid such as water with an ethylene glycol antifreeze through the cooling system of the engine and through an exhaust heat exchanger where heat is exchanged with the working fluid. The working fluid is then conveyed or pumped to another heat exchanger, or radiator, that is located in the air flow in the air conditioned building.
Patents which have addressed various aspects of the use of combustion engines (including turbines) are found in the prior art and include the following:
U.S. Pat. No. 4,592,208 Sollner et al. discloses a heating or cooling apparatus with an internal combustion engine enclosed in an insulating housing.
U.S. Pat. No. 4,510,762 Richarts reveals a heat recovery method wherein heat from an internal combustion engine is delivered to augment a heat pumping system.
U.S. Pat. No. 4,408,715 Gueneau relates to a heating installation for premises or residential or industrial use. U.S. Pat. No. 4,292,814 Braun shows a heat pump driven by a free piston engine with fans driven by compressed air.
U.S. Pat. No. 3,421,339 Volk et al. discloses a unidirectional heat pump system. Engine cooling water is used to heat the load, and temperature controlled valves control the amount of flow.
U.S. Pat. No. 3,139,924 Schreiner reveals an internal combustion engine driven heat pump system. A reversible fan blows air across the engine, radiator and refrigeration coil.
U.S. Pat. No. 3,135,318 Carleton relates to a heat pump system which has an internal combustion engine, i.e. a turbine.
As a matter of definition certain preferred terminology is to be used with meanings according to the following.
Within the context herein, an engine driven heat pump system means a system where a vapor compression heat pump is driven by a combustion prime mover of a type to provide motive power to the compressor. Operating in the heating mode means that the engine driven heat pump system is selectively arranged to provide a cooling effect at the outdoor evaporator heat exchanger, and a heating effect at the indoor condenser heat exchanger which is contacting the air of the air conditioned space.
The term "high ambient heating mode" is used to define outside air at temperatures greater than about 15.degree. to 40.degree. F. (-9.5.degree. to 4.5.degree. C.), so that the compressor is operating in a sufficiently loaded condition to pump enough refrigerant vapor for the engine to operate with sufficient load to produce excess heat to augment the heating load on the condenser.
The term "low ambient heating mode" relates to the operating conditions where the outside air as a source of heat is below about 15.degree. F.(-9.5.degree. C.) and the engine would be insufficiently loaded to produce an adequate amount of auxiliary heat to augment the condenser of the vapor compression heat pump system.
The purpose of this invention is to provide a simple way to furnish extra heat load to the vapor compression refrigerant system in an engine driven heat pump system during the low ambient heating mode.
In circumstances when it is advantageous to produce a larger load on the compressor and the engine by loading the engine in this way, the engine operates at a higher horsepower and thereby produces more auxiliary heat. The auxiliary heat is transferred to the engine working fluid which is then transferred to the air flow in the air conditioned building to provide additional heat. A feature of the invention is the provision of a flow proportioning valve in the engine working fluid circuit to divert some of the engine heat to a radiator which is in heat exchange relationship with the outside ambient air. In most instances, air flow will pass first through the engine radiator and then across the outside heat exchanger to increase the rate of transfer of the engine exhaust heat to the refrigerant sub-system in this cold ambient heating mode of operation.
Accordingly, the load on the compressor is increased as some auxiliary heat is transferred to the heat exchanger of the vapor compression subsystem which is operating as an evaporator in the heating mode. An advantage is that the evaporator is therefor operating at a higher temperature and the propensity to develop frost is reduced, thereby reducing another problem that plagues the operation of vapor compressor heat pumps operating under cold ambient outside air conditions.
Other benefits accrue from the increased evaporator temperatures and reduced pressure ratios, so that other types of refrigerants may be used, such as that known as R-12. In addition other types of compressors may become advantageous, such as rotary or sliding vane types.